1. Field of the Invention
The present invention relates to a low profile, surface-mounted connector having curved cantilevered spring contacts.
2. Description of the Prior Art
Surface-mounted connectors are known in the art. A board to board surface-mounted connector system using a receptacle housing having a low profile, that is, a housing with a height above the board of approximately 0.170 inch, and having single cantilevered spring contacts therein is manufactured and sold by Hirose Inc. as the HRS DF9 Series Board to Board connector.
U.S. Pat. No. 4,682,829 (Kunkle et al.) and U.S. Pat. No. 4,693,528 (Asick et al.) also disclose surface-mounted connectors.
In a typical female receptacle having single or dual cantilevered mounted electrical spring contacts, such as those shown in U.S. Pat. No. 4,955,820 (Yamada et al.), U.S. Pat. No. 4,025,147 (Van Arsdale et al.), U.S. Pat. No. 4,715,820 (Andrews Jr., et al.), U.S. Pat. No. 3,601,775 (Longenecker et al.), U.S. Pat. No. 4,734,060 (Kawawada et al.), and U.S. Pat. No. 4,420,215 (Tengler), the magnitude of the normal force exerted on the contact of a male plug by a spring contact in the receptacle is determined, for a predetermined spring constant, by the magnitude of the beam deflection undergone by the spring contact within the receptacle housing.
The receptacle housing within which the spring contact is disposed is typically fabricated by a molding process. As a result there can occur variations in the dimensions of the housing which could reduce the magnitude of the beam deflection of the spring.
In most cases, for a cantilevered mounted electrical spring contact having a beam length of greater than approximately 0.135 inch and a housing height of greater than approximately 0.170 inch, a sufficient level of normal force may still be exerted by the spring contact despite dimensional variations in the housing due to manufacture.
However, in an environment where the available spacing between adjacent boards is an important factor, as when connecting conductive tracings on the surface of one substrate to tracings disposed on the surface of an adjacent substrate spaced about 0.200 inches apart, as within a cellular telephone, the height (i.e., distance above the board) of both the housing of the male plug and the housing of the corresponding female receptacle, as well as the height of the mated plug and receptacle, become critical. With a low profile receptacle housing (that is, one with a height less than approximately 0.170 inch) the beam length and the magnitude of available beam deflection within the housing become limited. Thus, to maintain the same desired level of normal force as in a typical connector, the contact in the receptacle of reduced height must exhibit an increased spring rate. However, in such an instance the effect of dimensional variations in the manufacture of the housing becomes more pronounced. Loss of a unit length of beam deflection due to a dimensional variation of the housing results in a wider variation in normal force generated by the contact.
The following discussion of actual connectors should make the preceding point clearer. For a high profile connector typically with a height of approximately 0.250 inch, the cantilever beam length is approximately 0.215 inch. Assuming a spring rate of approximately 15 grams/per thousandths of an inch and a deflection of approximately 0.010 inch, the normal force exerted by the beam is on the order of 150 grams. For a loss of 0.002 inch of deflection due to manufacturing tolerances, approximately 30 grams of normal force is lost, leaving a normal force exerted by the contact of approximately 120 grams. In contrast, for a low profile connector typically with a height of approximately 0.170 inch, a cantilever beam length of approximately 0.135 inch, a spring rate of approximately 50 grams/per thousandths of an inch and a deflection of approximately 0.003 inch, the normal force exerted by the beam is also on the order of 150 grams. However, for the same loss of 0.002 inch of deflection due to manufacturing tolerances, approximately 100 grams of normal force is lost, leaving a normal force exerted by the contact of approximately 50 grams.
Accordingly, it is believed advantageous to provide an arrangement for a receptacle in which relatively large effective beam deflection is permitted despite the reduction in available housing dimensions, so that the normal force exerted by the spring contact of the receptacle remains within a predetermined range despite dimensional variations of the housing due to manufacturing tolerances.